In processing of a gear, gear chamfering is performed on a workpiece (gear to be cut) subjected to gear cutting in a bobbing machine or the like in some cases. The gear chamfering is processing of chamfering a tooth profile ridge section which is a corner portion formed by an end surface and tooth surfaces of the workpiece.
There is a method of gear chamfering in which chamfering (rolling) is performed by pressing a phrasing cutter being a gear chamfering tool against the tooth profile ridge section of the workpiece to crush the tooth profile ridge section. When the tooth profile ridge section is chamfered by rolling as described above, raised portions are formed in the tooth surfaces by the crushing of the tooth profile ridge section, and this may affect tooth surface accuracy of the workpiece.
Then, there is a method of gear chamfering in which chamfering (cutting) is performed by, instead of rolling with the phrasing cutter, making a cutting tool being the gear chamfering tool cut into the tooth profile ridge section of the workpiece to cut the tooth profile ridge section (for example, Patent Document 1). Operations of the cutting tool in such gear chamfering by cutting are illustrated in an explanatory diagram of FIG. 5. In the gear chamfering by cutting, as illustrated in FIG. 5, a not-illustrated crank mechanism causes a cutting tool 144 (cutting edge portion 156 of the cutting tool 144) to perform a reciprocation drawing an arc-shaped (substantially linear) trajectory T156, and the cutting edge portion 156 of the cutting tool 144 is made to cut into a tooth profile ridge section WR of a workpiece W.
In this reciprocation of the cutting tool 144, the cutting edge portion 156 of the cutting tool 144 moves from an initial position L100 distant from the workpiece W toward the workpiece W (leftward in FIG. 5) while drawing the arc-shaped trajectory T156, cuts (chamfers) the tooth profile ridge section WR after passing an entrance position L101 where the cutting edge portion 156 enters a portion between tooth surfaces Ws of the workpiece W, reaches a turn-around position L102 after the cutting (chamfering), and then returns to the initial position L100 while drawing the same arc-shaped trajectory T156.
When the cutting edge portion 156 of the cutting tool 144 is located in an operation area A101 between the initial position L100 and the entrance position L101, no cutting tool 144 is located in the portion between the tooth surfaces WS of the workpiece W. Accordingly, there is no risk of interference between the workpiece W and the cutting tool 144 even if the workpiece W is rotationally driven. However, when the cutting edge portion 156 of the cutting tool 144 is located in an operation area A102 between the entrance position L101 and the turn-around position L102, at least part of the cutting tool 144 is located in the portion between the tooth surfaces Ws of the workpiece W. Accordingly, the workpiece W and the cutting tool 144 interfere with each other if the workpiece W is rotationally driven. Thus, although the workplace W can be rotationally driven when the cutting edge portion 156 of the cutting tool 144 is located in the operation area A101, the workpiece W cannot be rotationally driven when the cutting edge portion 156 of the cutting tool 144 is located in the operation area A102, and the rotation of the workplace W has to be stopped.
In other words, in the gear chamfering by the cutting using the cutting tool 144, the chamfering is performed on the tooth profile ridge section HR of the workpiece W by causing the cutting tool 144 to perform the reciprocation such that the cutting edge portion 156 of the cutting tool 144 draws the arc-shaped trajectory T156, and by intermittently rotationally driving the workpiece W when the cutting edge portion 156 of the cutting tool 144 is located in the operation area A101.